MEASUREMENT OF THERMAL-DIFFUSIVITY OF THE REFRIGERANTS R22 AND R134A BY MEANS OF DYNAMIC LIGHT-SCATTERING

Dynamic light scattering is an efficient method of determining thermal diffusivity of transparent fluids in a wide region of state, its main advantage over conventional methods being the fact of thermodynamic equilibrium within the sample. This paper presents new thermal diffusivity measurements of the environmentally acceptable refrigerants R22 and R134a, the latter substance being a possible substitute for the refrigerant R12. Measurements were carried out along the critical isochore, both coexisting phases and up to seven isotherms within a range of state characterized in terms of reduced pressure and density as 0.5 < p/p(c) < 3.0 and 0.2 < rho/rho(c) < 2.3 respectively, amounting to a total of 300 measurement points per substance. Provided an equation of state to determine c(p), the diffusivity data can also be expressed in terms of thermal conductivity lambda.